The present invention relates to internal combustion engines, and, more particularly, to a method of controlling generation of nitrogen oxides in an internal combustion engine.
An internal combustion engine generally is of two basic types, i.e., a spark ignition engine and a compression combustion engine. A spark ignition engine uses a spark plug to ignite the fuel and air mixture which is injected into the combustion chamber. A compression combustion engine utilizes the energy resulting from compression of the fuel and air mixture as the piston travels toward a top dead center position within the combustion cylinder to ignite the fuel and air mixture. Regardless of whether the internal combustion engine is a spark ignition engine or a compression combustion engine, it is desirable to control the point in time at which combustion occurs relative to the position of the piston within the combustion cylinder.
Cycle-to-cycle variations in the combustion event are undesirable characteristics of operating and running a spark ignition engine. The causes of these combustion variations have been attributed to variations in the air/fuel mixture, motion or turbulence (especially in the vicinity of the spark plug), fuel and air charging, and fresh air and residual mixing. The results of these combustion variations are variations in work output or indicated mean effective pressure (IMEP), combustion efficiency, and emissions on a cycle-to-cycle basis (such as nitrogen oxides (NOx)). These combustion variations can manifest themselves in a variety of ways including randomly varying misfires, slow burns, partial burns and fast burns, including detonation or knock. These phenomena are generally more evident under high throttle, high exhaust gas recirculation (EGR), low speed, low turbulence, cold start and lean air/fuel ratio engine operation conditions.
The timing of spark ignition is important in obtaining maximum or desired efficiency and proper operating characteristics of the internal combustion engine. It is also generally understood that the resultant combustion event is a function of ignition and early flame development, and a poor combustion event is known to be primarily a function of those conditions that are present in that individual cycle.
It is known to provide a plurality of pressure sensors which sense pressures within respective combustion cylinders at discrete points in time for the purpose of analyzing a combustion event. Signals from the pressure sensors may be transmitted to an Electronic Control Module (ECM) for the purpose of controlling the timing of the combustion event within the combustion cylinder as the piston reciprocates between a bottom dead center position and a top dead center position. Sensing pressures within combustion cylinders for the purpose of controlling the timing of the engine is disclosed, e.g., in U.S. Pat. Nos. 4,063,538 (Powell et al.), 4,736,724 (Hamburg et al.), 5,276,625 (Nakaniwa), and 5,359,833 (Baldwin et al.). Examples of pressure sensors which withstand the harsh operating environment in a combustion cylinder are disclosed in U.S. Pat. Nos. 5,714,680 (Taylor et al.), 5,452,087 (Taylor et al.), and 5,168,854 (Hashimoto et al.).
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, a method of controlling generation of nitrogen oxides in an internal combustion engine is provided with the steps of: combusting a fuel and air mixture within a combustion cylinder; determining a pressure in the combustion cylinder and a position of a piston within the combustion cylinder; calculating an amount of nitrogen oxides generated with the combusting step, dependent upon the determining step; storing a history of the calculated amount of nitrogen oxides in a memory device; and controlling an output action, dependent upon the calculated amount of nitrogen oxides, the stored history of nitrogen oxides and a threshold value of the nitrogen oxides.